jenkins do report git commit date based on master timezone, not using committer timezone.

For sample, Committer date is reported by raw changelog as `1424725127 -0500`
This is parsed by git-plugin ChangelogParser as `iso.format(1424725127) + remaining string`

If jenkins master run as UTC+1 (Fr) this will result into : `2015-02-23T21:58:47+0100 -0500` which is wrong